Table saw with improved safety system

ABSTRACT

A table saw having a brake mechanism configured to engage and stop a blade is disclosed. The table saw includes a brake positioning system configured to adjust the position of the brake mechanism to maintain the brake mechanism in an operative position relative to the blade as the blade is raised and lowered.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/542,938, filed Oct. 2, 2006, which is a continuation of a number ofpatent applications, including Ser. No. 11/348,580, filed Feb. 6, 2006now abandoned, which in turn is a continuation of Ser. No. 10/052,705,filed Jan. 16, 2002, issuing as U.S. Pat. No. 6,994,004 on Feb. 7, 2006,which in turn is a continuation-in-part of the following U.S. patentapplications: Ser. No. 09/676,190, filed Sep. 29, 2000 now U.S. Pat. No.7,055,417, Ser. No. 09/929,221, filed Aug. 13, 2001 now U.S. Pat. No.7,284,467, Ser. No. 09/929,226, filed Aug. 13, 2001, issued as U.S. Pat.No. 6,920,814 on Jul. 26, 2005, Ser. No. 09/929,227, filed Aug. 13, 2001now U.S. Pat. No. 7,308,843, Ser. No. 09/929,234, filed Aug. 13, 2001now U.S. Pat. No. 7,225,712, Ser. No. 09/929,235, filed Aug. 13, 2001now U.S. Pat. No. 7,350,444, Ser. No. 09/929,236, filed Aug. 13, 2001now U.S. Pat. No. 7,610,836, Ser. No. 09/929,237, filed Aug. 13, 2001now U.S. Pat. No. 7,600,455, Ser. No. 09/929,238, filed Aug. 13, 2001now abandoned, Ser. No. 09/929,240, filed Aug. 13, 2001 now U.S. Pat.No. 7,100,483, Ser. No. 09/929,241, filed Aug. 13, 2001 now U.S. Pat.No. 7,024,975, Ser. No. 09/929,242, filed Aug. 13, 2001 now U.S. Pat.No. 7,509,899, Ser. No. 09/929,244, filed Aug. 13, 2001, issued as U.S.Pat. No. 6,857,345 on Feb. 22, 2005, Ser. No. 09/929,425, filed Aug. 13,2001 now U.S. Pat. No. 7,137,326, and Ser. No. 09/929,426, filed Aug.13, 2001 now U.S. Pat. No. 7,210,383. The disclosures of all theseapplications are hereby incorporated by reference in their entireties.

U.S. patent application Ser. No. 10/052,705 also claims the benefit ofand priority from the following U.S. Provisional Patent Applications:Ser. No. 60/270,011, filed Feb. 20, 2001, Ser. No. 60/270,941, filedFeb. 22, 2001, Ser. No. 60/270,942, filed Feb. 22, 2001, Ser. No.60/273,177, filed Mar. 2, 2001 and Ser. No. 60/273,178, filed Mar. 2,2001. The disclosures of all these applications are hereby incorporatedby reference in their entireties.

U.S. patent application Ser. No. 11/348,580 is also a continuation ofthe following U.S. patent applications: Ser. No. 10/100,211, filed Mar.13, 2002, Ser. No. 10/146,527, filed May 15, 2002, Ser. No. 10/172,553,filed Jun. 13, 2002 now U.S. Pat. No. 7,231,856, Ser. No. 10/189,027,filed Jul. 2, 2002 now U.S. Pat. No. 7,712,403, Ser. No. 10/189,031,filed Jul. 2, 2002 now U.S. Pat. No. 7,171,879, Ser. No. 10/202,928,filed Jul. 25, 2002 now U.S. Pat. No. 7,000,514, Ser. No. 10/243,042,filed Sep. 13, 2002 now U.S. Pat. No. 7,197,969, Ser. No. 10/292,607,filed Nov. 12, 2002 now U.S. Pat. No. 7,077,039, Ser. No. 10/341,260,filed Jan. 13, 2003 now abandoned, Ser. No. 10/345,630, filed Jan. 15,2003 now abandoned, Ser. No. 10/643,296, filed Aug. 18, 2003 nowabandoned, Ser. No. 10/785,361, filed Feb. 23, 2004 now U.S. Pat. No.6,997,090, Ser. No. 10/794,161, filed Mar. 4, 2004 now U.S. Pat. No.7,098,800, Ser. No. 10/923,273, filed Aug. 20, 2004 now U.S. Pat. No.7,350,445, Ser. No. 10/923,282, filed Aug. 20, 2004 now abandoned, Ser.No. 10/923,290, filed Aug. 20, 2004 now U.S. Pat. No. 7,472,634, Ser.No. 10/932,339, filed Sep. 1, 2004 now U.S. Pat. No. 7,290,472, Ser. No.11/026,006, filed Dec. 31, 2004, Ser. No. 11/026,114, filed Dec. 31,2004 now U.S. Pat. No. 7,707,920, Ser. No. 11/027,254, filed Dec. 31,2004 now abandoned, Ser. No. 11/027,322, filed Dec. 31, 2004 nowabandoned, Ser. No. 11/027,600, filed Dec. 31, 2004 now U.S. Pat. No.7,536,238, Ser. No. 11/045,972, filed Jan. 28, 2005, Ser. No.11/098,984, filed Apr. 4, 2005 now U.S. Pat. No. 7,353,737, Ser. No.11/107,499, filed Apr. 15, 2005 now U.S. Pat. No. 7,481,140, Ser. No.11/208,214, filed Aug. 19, 2005, and Ser. No. 11/256,757, filed Oct. 24,2005. The disclosures of all these applications are hereby incorporatedby reference in their entireties.

U.S. patent application Ser. No. 11/348,580 also claims the benefit ofand priority from U.S. Provisional Patent Application Ser. No.60/667,485, filed Mar. 31, 2005, the disclosure of which is herebyincorporated by reference in its entirety.

FIELD

The present invention relates to table saws and more particularly to atable saw with an improved safety system.

BACKGROUND

Table saws are a type of woodworking machinery used to cut workpieces ofwood, plastic and other materials. Table saws include a flat surface ortable with a circular saw blade extending up through a slot in thetable. A user slides a workpiece on the table against and past the bladewhile the blade is spinning to cut the workpiece.

Of all the tools in a woodworking shop, table saws present perhaps thegreatest risk of injury. Table saws present a risk of injury to usersbecause the spinning blade is often exposed when in use. The blade cutsvery quickly and can sever a finger upon the slightest slip ormisplacement. Accordingly, safety features or systems have beendeveloped to minimize the risk of injury. Probably the most commonsafety feature is a blade guard that physically blocks a user frommaking contact with the spinning blade. In many situations, blade guardseffectively reduce the risk of injury; however, there are many instanceswhere the nature of the operations to be performed precludes using aguard that completely blocks access to the blade.

There exists a need for a table saw with a safety system thatsignificantly reduces the risk of serious injury to a user accidentallycontacting the spinning blade. The present invention provides such atable saw.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a table saw with a fast-actingsafety system.

FIG. 2 is a schematic diagram of an exemplary safety system configuredto stop the blade of a table saw.

FIG. 3 shows an exemplary table saw.

FIG. 4 is a fragmentary schematic side elevation of one exemplary brakemechanism configured to stop the rotation of the blade on a table saw.

FIG. 5 is a fragmentary cross-sectional schematic view taken generallyalong line 5-5 in FIG. 4.

FIG. 6 is similar to FIG. 5 but the support brace has been removed tofurther illustrate other portions of the brake mechanism and table saw.

FIG. 7 is a fragmentary schematic side elevation of an alternativeexemplary brake mechanism configured to stop the rotation of the bladeon a table saw.

FIG. 8 is a fragmentary cross-sectional schematic view taken generallyalong line 8-8 in FIG. 7.

FIG. 9 is a magnified, cross-sectional schematic view showing engagementof the shaft with the support brace, positioning member and cartridge.For clarity, the shaft is not shown in cross-section.

FIG. 10 is a fragmentary schematic side elevation of another alternativeexemplary brake mechanism configured to stop rotation of the blade on atable saw.

FIG. 11 is similar to FIG. 10 but shows the rack assembly removed tobetter illustrate the motion of the cartridge and brake pawl as theheight of the blade is adjusted.

FIG. 12 is a fragmentary cross-sectional schematic view taken generallyalong line 12-12 in FIG. 10.

FIG. 13 is a fragmentary schematic side elevation of an alternativeembodiment for rotationally coupling the cartridge and brake pawl to thepositioning member.

FIG. 14 is a rear view of the embodiment of FIG. 13.

FIG. 15 is a top view of the embodiment of FIG. 13.

FIG. 16 is a fragmentary schematic side elevation of an alternativeembodiment for rotationally coupling the cartridge and brake pawl to thepositioning member.

FIG. 17 is a rear view of the embodiment of FIG. 16.

FIG. 18 is a fragmentary schematic side elevation of an alternativeembodiment for rotationally coupling the cartridge and brake pawl to thepositioning member.

DETAILED DESCRIPTION AND BEST MODE

A table saw according to the present invention is shown schematically inFIG. 1 and indicated generally at 10. Table saw 10 may be any of avariety of different types and configurations of table saw adapted forcutting workpieces, such as wood, plastic, etc. Table saw 10 includes anoperative structure 12 having a cutting tool 14 and a motor assembly 16adapted to drive the cutting tool. Table saw 10 also includes a safetysystem 18 configured to minimize the potential of a serious injury to aperson using table saw 10. Safety system 18 is adapted to detect theoccurrence of one or more dangerous, or triggering, conditions duringuse of table saw 10. If such a dangerous condition is detected, safetysystem 18 is adapted to engage operative structure 12 to limit anyinjury to the user caused by the dangerous condition.

Table saw 10 also includes a suitable power source 20 configured toprovide power to operative structure 12 and safety system 18. Powersource 20 may be an external power source such as line current, or aninternal power source such as a battery. Alternatively, power source 20may include a combination of both external and internal power sources.Furthermore, power source 20 may include two or more separate powersources, each adapted to power different portions of table saw 10.

Motor assembly 16 includes one or more motors adapted to drive cuttingtool 14. The motors may be either directly or indirectly coupled to thecutting tool. Cutting tool 14 typically includes one or more blades orother suitable cutting implements that are adapted to cut or removeportions from the workpieces. The particular form of cutting tool 14will vary depending upon the various embodiments of table saw 10 and/orthe workpieces being cut.

Safety system 18 includes a detection subsystem 22, a reaction subsystem24 and a control subsystem 26. Control subsystem 26 may be adapted toreceive inputs from a variety of sources including detection subsystem22, reaction subsystem 24, operative structure 12 and motor assembly 16.The control subsystem may also include one or more sensors adapted tomonitor selected parameters of table saw 10. In addition, controlsubsystem 26 typically includes one or more instruments operable by auser to control the table saw. The control subsystem is configured tocontrol table saw 10 in response to the inputs it receives.

Detection subsystem 22 is configured to detect one or more dangerous, ortriggering, conditions during use of table saw 10. For example, thedetection subsystem may be configured to detect that a portion of theuser's body is dangerously close to, or in contact with, a portion ofcutting tool 14. As another example, the detection subsystem may beconfigured to detect the rapid movement of a workpiece due to kickbackby the cutting tool, as is described in U.S. Provisional PatentApplication Ser. No. 60/182,866, filed Feb. 16, 2000 and U.S. patentapplication Ser. No. 09/676,190, filed Sep. 29, 2000, the disclosures ofwhich are herein incorporated by reference. In some embodiments,detection subsystem 22 may inform control subsystem 26 of the dangerouscondition, which then activates reaction subsystem 24. In otherembodiments, the detection subsystem may be adapted to activate thereaction subsystem directly.

Once activated in response to a dangerous condition, reaction subsystem24 is configured to engage operative structure 12 quickly to preventserious injury to the user. It will be appreciated that the particularaction to be taken by reaction subsystem 24 will vary depending on thetype of table saw 10 and/or the dangerous condition that is detected.Further, the reaction subsystem may be configured to take a combinationof steps to protect the user from serious injury. For example, reactionsubsystem 24 may be configured to do one or more of the following: stopthe movement of cutting tool 14, disconnect motor assembly 16 from powersource 20, place a barrier between the cutting tool and the user, orretract the cutting tool from its operating position, etc. Placement ofa barrier between the cutting tool and teeth is described in more detailin U.S. Provisional Patent Application Ser. No. 60/225,206, filed Aug.14, 2000 and U.S. patent application Ser. No. 09/929,226, filed Aug. 13,2001, the disclosures of which are herein incorporated by reference.Retraction of the cutting tool from its operating position is describedin more detail in U.S. Provisional Patent Application Ser. No.60/225,089, filed Aug. 14, 2000 and U.S. patent application Ser. No.09/929,242, filed Aug. 13, 2001, the disclosures of which are hereinincorporated by reference.

The configuration of reaction subsystem 24 typically will vary dependingon which action(s) are taken. In the exemplary embodiment depicted inFIG. 1, reaction subsystem 24 is configured to stop the movement ofcutting tool 14 and includes a brake mechanism 28, a biasing mechanism30, a restraining mechanism 32, and a release mechanism 34. Brakemechanism 28 is adapted to engage operative structure 12 under theurging of biasing mechanism 30. During normal operation of table saw 10,restraining mechanism 32 holds the brake mechanism out of engagementwith the operative structure. However, upon receipt of an activationsignal by control subsystem 26, the brake mechanism is released from therestraining mechanism by release mechanism 34, whereupon, the brakemechanism quickly engages at least a portion of the operative structureto bring the cutting tool to a stop.

It will be appreciated by those of skill in the art that the exemplaryembodiment depicted in FIG. 1 and described above may be implemented ina variety of ways depending on the type and configuration of operativestructure 12. Turning attention to FIG. 2, one example of the manypossible implementations of table saw 10 includes a cutting tool 14 inthe form of a circular blade 40 mounted on a rotating shaft or arbor 42.Blade 40 includes a plurality of cutting teeth (not shown) disposedaround the outer edge of the blade. As described in more detail below,braking mechanism 28 is adapted to engage the teeth of blade 40 and stopthe rotation of the blade.

In the exemplary implementation, detection subsystem 22 is adapted todetect the dangerous condition of the user coming into contact withblade 40. The detection subsystem includes a sensor assembly havingcontact detection electrodes 44 and 46, capacitively coupled to blade 40to detect any contact between the user's body and the blade. Typically,the blade, or some larger portion of cutting tool 14 is electricallyisolated from the remainder of table saw 10. Alternatively, detectionsubsystem 22 may include a different sensor assembly configured todetect contact in other ways, such as optically, resistively, etc. Inany event, the detection subsystem is adapted to transmit a signal tocontrol subsystem 26 when contact between the user and the blade isdetected. Various exemplary embodiments and implementations of detectionsubsystem 22 are described in more detail in U.S. Provisional PatentApplication Ser. No. 60/225,200, filed Aug. 14, 2000, U.S. patentapplication Ser. No. 09/929,426, filed Aug. 13, 2001, U.S. ProvisionalPatent Application Ser. No. 60/225,211, filed Aug. 14, 2000 and U.S.patent application Ser. No. 09/929,221, filed Aug. 13, 2001, thedisclosures of which are herein incorporated by reference.

Control subsystem 26 includes one or more instruments 48 that areoperable by a user to control the motion of blade 40. Instruments 48 mayinclude start/stop switches, speed controls, direction controls, etc.Control subsystem 26 also includes a logic controller 50 connected toreceive the user's inputs via instruments 48. Logic controller 50 isalso connected to receive a contact detection signal from detectionsubsystem 22. Further, the logic controller may be configured to receiveinputs from other sources (not shown) such as blade motion sensors,workpiece sensors, etc. In any event, the logic controller is configuredto control operative structure 12 in response to the user's inputsthrough instruments 48. However, upon receipt of a contact detectionsignal from detection subsystem 22, the logic controller overrides thecontrol inputs from the user and activates reaction subsystem 24 to stopthe motion of the blade. Various exemplary embodiments andimplementations of control subsystem 26 are described in more detail inU.S. Provisional Patent Application Ser. No. 60/225,059, filed Aug. 14,2000, U.S. patent application Ser. No. 09/929,237, filed Aug. 13, 2001,U.S. Provisional Patent Application Ser. No. 60/225,094, filed Aug. 14,2000 and U.S. patent application Ser. No. 09/929,234, filed Aug. 13,2001, the disclosures of which are herein incorporated by reference.

In the exemplary implementation shown in FIG. 2, brake mechanism 28includes a pawl 60 mounted adjacent the edge of blade 40 and selectivelymoveable to engage and grip the teeth of the blade. Pawl 60 may beconstructed of any suitable material adapted to engage and stop theblade. As one example, the pawl may be constructed of a relatively highstrength thermoplastic material such as polycarbonate, ultrahighmolecular weight polyethylene (UHMW), Acrylonitrile Butadiene Styrene(ABS), etc., or a metal such as aluminum, etc. It will be appreciatedthat the construction of pawl 60 will vary depending on theconfiguration of blade 40. In any event, the pawl is urged into theblade by a biasing mechanism in the form of a spring 66. In theimplementation shown in FIG. 2, pawl 60 is pivoted into the teeth ofblade 40. It should be understood that sliding or rotary movement ofpawl 60 may also be used. The spring is adapted to urge pawl 60 into theteeth of the blade with sufficient force to grip the blade and quicklybring it to a stop.

The pawl is held away from the edge of the blade by a restraining memberin the form of a fusible member 70. The fusible member is constructed ofa suitable material adapted to restrain the pawl against the bias ofspring 66, and also adapted to melt under a determined electricalcurrent density. Examples of suitable materials for fusible member 70include NiChrome wire, stainless steel wire, etc. The fusible member isconnected between the pawl and a contact mount 72. Preferably, member 70holds the pawl relatively close to the edge of the blade to reduce thedistance pawl 60 must travel to engage blade 40. Positioning the pawlrelatively close to the edge of the blade reduces the time required forthe pawl to engage and stop the blade. Typically, the pawl is heldapproximately 1/32-inch to ¼-inch from the edge of the blade by fusiblemember 70; however other pawl-to-blade spacings may also be used withinthe scope of the invention.

Pawl 60 is released from its unactuated, or cocked, position to engageblade 40 by a release mechanism in the form of a firing subsystem 76.The firing subsystem is coupled to contact mount 72, and is configuredto melt fusible member 70 by passing a surge of electrical currentthrough the fusible member. Firing subsystem 76 is coupled to logiccontroller 50 and activated by a signal from the logic controller. Whenthe logic controller receives a contact detection signal from detectionsubsystem 22, the logic controller sends an activation signal to firingsubsystem 76, which melts fusible member 70, thereby releasing the pawlto stop the blade. Various exemplary embodiments and implementations ofreaction subsystem 24 are described in more detail in U.S. ProvisionalPatent Application Ser. No. 60/225,056, filed Aug. 14, 2000, U.S. patentapplication Ser. No. 09/929,240, filed Aug. 13, 2001, U.S. ProvisionalPatent Application Ser. No. 60/225,170, filed Aug. 14, 2000, U.S. patentapplication Ser. No. 09/929,227, filed Aug. 13, 2001, U.S. ProvisionalPatent Application Ser. No. 60/225,169, filed Aug. 14, 2000 and U.S.patent application Ser. No. 09/929,241, filed Aug. 13, 2001, thedisclosures of which are herein incorporated by reference.

It will be appreciated that activation of the brake mechanism mayrequire the replacement of one or more portions of safety system 18. Forexample, pawl 60 and fusible member 70 typically must be replaced beforethe safety system is ready to be used again. Thus, it may be desirableto construct one or more portions of safety system 18 in a cartridgethat can be easily replaced. For example, in the exemplaryimplementation depicted in FIG. 2, safety system 18 includes areplaceable cartridge 80 having a housing 82. Pawl 60, spring 66,fusible member 70 and contact mount 72 are all mounted within housing82. Alternatively, other portions of safety system 18 may be mountedwithin the housing. In any event, after the reaction system has beenactivated, the safety system can be reset by replacing cartridge 80. Theportions of safety system 18 not mounted within the cartridge may bereplaced separately or reused as appropriate. Various exemplaryembodiments and implementations of a safety system using a replaceablecartridge are described in more detail in U.S. Provisional PatentApplication Ser. No. 60/225,201, filed Aug. 14, 2000, U.S. patentapplication Ser. No. 09/929,236, filed Aug. 13, 2001, U.S. ProvisionalPatent Application Ser. No. 60/225,212, filed Aug. 14, 2000 and U.S.patent application Ser. No. 09/929,244, filed Aug. 13, 2001, thedisclosures of which are herein incorporated by reference.

Turning attention now to FIG. 3, one exemplary type of table saw, oftencalled a contractor's saw, is shown in more detail. Table saw 10includes a table 84 through which a blade 40 extends from beneath thetable. The table and blade are supported by a housing 86 and legs 88.Housing 86 encloses the mechanics that support, position and drive theblade. A motor to drive the blade can be positioned in or outside thehousing. A switch 48 turns the saw on and off, causing blade 40 torotate. Handles, such as handle 90, are used to adjust the position ofthe blade relative to the table, for example, how far the blade extendsabove the table or how the blade tilts relative to the top of the table.Of course, table saws take many different configurations, from largesaws sized for industrial use to small saws that can be placed on abench top or counter, and table saws come with various types of tablesand housings.

It will be appreciated that reaction subsystem 24 may be configured andmounted in a variety of different ways to stop the rotation of blade 40.Typically, the reaction subsystem is configured to stop the bladeregardless of the position (i.e., height and tilt) of the blade. In someembodiments such as described in the references incorporated herein, thebrake mechanism is shaped to engage the blade at any height and/or tiltangle. In alternative embodiments, the position of the brake mechanismis coupled to move along with the blade so that the blade is stationaryrelative to the brake mechanism. Examples of such embodiments are alsodescribed in the incorporated references. As a further alternative,brake mechanism 28 may be configured to move separately from the bladewhile maintaining a constant orientation adjacent the perimeter of theblade. One exemplary implementation of such an alternative embodiment isillustrated in FIGS. 4-6.

In the depicted embodiment, blade 40 is mounted on an arbor 42 by a nut43. The arbor spins the blade in the direction indicated. Table 84 whichdefines the work surface for the table saw, is adjacent the blade andthe blade is selectively extendable above the table as shown. An arborblock 92 supports arbor 42 and holds the arbor in bearings to allow thearbor to rotate. The arbor is connected to a motor (not shown), such asby a belt extending around a pulley on the arbor and a pulley on themotor's drive shaft, and the motor drives or spins the arbor, as isknown in the art.

Arbor block 92 is mounted on a pin 94 and may pivot around that pin.Arbor block 92 is configured to pivot up and down so that a user canraise and lower the blade relative to the table as needed. A portion ofarbor block 92 defines a gear segment 96. Table saw 10 includes a firstworm gear control member 98, configured to engage and drive gear segment96. First worm gear control member 98 is attached to a handle 90. A useradjusts the vertical position of blade 40 by turning the first worm gearcontrol member via the handle. Alternatively, table saw 10 may beconfigured in other ways to adjust the height of the blade, such as areknown to those of skill in the art.

Pin 94 is mounted to a first support member 100 that, along with asecond support member 102, comprise at least part of a support frame104. The support frame also includes one or more cross braces 106extending between lower portions of the first and second support membersto connect the support members together. The upper portions of the firstand second support members are pivotally coupled to table 84. A pair ofsupport brackets 108 extend downward from the lower surface of the tableadjacent each of the first and second support members. Each supportmember includes a projection 110 adapted to fit within and ride along anarcuate track (not shown) defined in each corresponding bracket 108. Thearcuate tracks define a pivot axis at or near the top surface of table84. As a result, support frame 104 is pivotal about the top of table 84to tilt blade 40. A portion of first support member 100 defines a gearsegment 112. Table saw 10 includes a second worm gear control member114, configured to engage and drive gear segment 112. Second worm gearcontrol member 114 is attached to a handle 90. A user adjusts the tiltof blade 40 by turning the second worm gear control member via thehandle. Alternatively, table saw 10 may be configured in other ways toadjust the tilt of the blade, such as are known to those of skill in theart.

Brake mechanism 28 includes a support brace 116 pivotally coupled tosupport frame 104. In the depicted embodiment, support brace 116includes a lower fork structure 118 pivotally mounted onto a pivot pin120. The pivot pin is supported by a collar 122 mounted on one of crossbraces 106. Pivot pin 120 is aligned generally perpendicular to blade 40so that support brace 116 pivots adjacent and parallel to the blade.

Support brace 116 also includes an upper fork structure 124 coupled to ashaft 126 that extends through the upper fork structure in a directionperpendicular to blade 40. Shaft 126 is adapted to support cartridge 80and one or more brake pawls 60 adjacent the perimeter of blade 40.Alternatively, cartridge 80 may be omitted. The brake pawl is formed todefine an orifice 128 adapted to slide onto, and rotate about, shaft126. The brake pawl is positionable on shaft 126 to be selectivelypivotal into the teeth of the blade. A restraining mechanism holds thebrake pawl away from the blade against the urging of a biasingmechanism. When a dangerous condition is detected, a release mechanismreleases the brake pawl from the restraining mechanism to pivot into theblade. Typically, the blade is stopped within approximately 2-5milliseconds. Exemplary restraining mechanisms, biasing mechanisms,release mechanisms, cartridges and brake pawls are described above andin the incorporated references.

Brake mechanism 28 also includes a positioning member 130 configured tomaintain the cartridge and brake pawl in a constant orientation adjacentthe perimeter of the blade. In the exemplary embodiment, positioningmember 130 includes a collar structure 132 adapted to fit around, andpivot about, a cylindrical channel 134 defined in arbor block 92. Collarstructure 132 may be formed by two or more semi-cylindrical segmentsconnectable together by bolts, etc. Such a construction would facilitatethe positioning of the collar structure around the arbor block.Alternatively, the collar structure may be connected to the arbor blockin any other suitable manner.

In any event, channel 134 is generally symmetrical about the elongatecentral axis of arbor 42. As a result, positioning member 130 is pivotalabout the arbor. The positioning member also includes a fork structure136 adapted to fit around shaft 126. Thus, the positioning member iscoupled to support brace 116 and brake pawl 60 by shaft 126.

As arbor block 92 is pivoted to raise and lower the blade, positioningmember 130 rotates around the arbor block in channel 134 and pivotssupport brace 116 toward and away from second support member 102,thereby maintaining shaft 126 at a constant radial distance from thearbor. In addition, positioning member 130 is rotationally coupled tocartridge 80 and/or brake pawl 60 so that the angle between positioningmember 130 and brake pawl 60 does not change. Therefore, while the brakepawl and cartridge travel in an arc defined by pivot pin 120 and supportbrace 116, the orientation of the brake pawl relative to the arbor andthe perimeter of the blade does not change as the height of the blade isadjusted.

In the exemplary embodiment, the cartridge and brake pawl arerotationally coupled to the positioning member by one or more nuts 138adapted to engage threads on each end of shaft 126. When tightened, nuts138 clamp the cartridge against fork structure 136 to produce africtional contact between the cartridge and fork structure 136.Alternatively, the cartridge and/or brake pawl may be rotationallycoupled to the positioning member in a variety of other ways, such aswill be described in more detail below.

Since the radial distance and orientation of the brake pawl does notchange relative to the blade, the brake pawl may be spaced very close tothe edge of the blade to minimize the time required to pivot the brakepawl into the blade. The close spacing between the brake pawl and theblade edge is maintained throughout the full range of adjustment of theblade. Further, since the brake mechanism is mounted on support frame104, the brake pawl also maintains a constant position when the blade istilted.

Upon receipt of an activation signal from control subsystem 26, brakepawl 60 is pivoted into the teeth of blade 40 by a biasing mechanism(not shown) such as described above. The blade cuts into the brake pawlcausing the brake pawl to pivot further into the blade until the bladebinds and stops. The force of the moving blade is transferred throughthe brake pawl to shaft 126. The direction of the force on shaft 126will vary depending on the height of the blade when the brake pawl istriggered.

It should be noted that in the exemplary embodiment, brake pawl 60 ispositioned at the back of the blade (i.e., between the blade and therear of table saw 10). It is believed that this arrangement will tend tocause blade 40 to move at least slightly downward as it rides down theface of the brake pawl. The clockwise (as viewed in FIG. 4) angularmomentum of the blade may be at least partially transferred topositioning member 130 which links arbor 42 and shaft 126. Thus, shaft126 is urged to move in a clockwise direction about the arbor. Since theshaft is constrained by support brace 116, the shaft tends to pivotgenerally horizontally toward first support member 100, thereby pushingthe arbor downward. Typically, blade 40 is prevented from significantdownward retraction during braking by the engagement of first worm gearcontrol member 98 with gear segment 96. Alternatively, at least aportion of first worm gear control member 98 may be configured torelease gear segment 96 to allow the arbor block to pivot downward,thereby retracting the blade below table 84.

As best seen in FIGS. 5 and 6, shaft 126 is supported on only one sideof the blade. While this facilitates the installation and removal of thebrake pawl and cartridge, a substantial amount of bending force will beproduced on the end of the shaft when the brake pawl pivots into theblade. By coupling to the shaft at two spaced-apart locations, upperfork structure 124 provides stability to the shaft during braking.Likewise, fork structure 136 is coupled to the shaft at two-spaced apartlocations to provide increased stability. Alternatively, shaft 126 maybe supported on both sides of blade 40. One example of such anembodiment is illustrated in FIGS. 7-9.

As best seen in FIG. 8, support brace 116 includes an inner arm 140 andan outer arm 142. The upper end of inner arm 140 is coupled to shaft 126on the side of the blade adjacent arbor block 92, while the upper end ofouter arm 142 is coupled to the shaft on the side of the blade oppositethe arbor block. Cartridge 80 and brake pawl 60 are mounted on shaft 126between the inner and outer arms of support brace 116. The lower ends ofthe inner and outer arms are mounted on pivot pin 120. A spacer 144disposed on the pivot pin maintains an equal distance between the upperand lower ends of the inner and outer arms. Pivot pin 120 is mounted ina pair of bearing structures 146, one on each cross brace 106.

The lower end of positioning member 130 is coupled to arbor 42 by abearing (not shown) that allows the arbor to rotate relative to thepositioning member. The upper end of the positioning member is connectedto shaft 126. In the exemplary embodiment, positioning member 130 isconnected to shaft 126 at a single point between inner arm 140 and outerarm 142. As shown in FIG. 9, the cartridge is clamped between thepositioning member and a shoulder portion 148 of shaft 126. The shaftincludes a threaded portion 150 which engages a threaded bore throughthe positioning member to rotationally couple the cartridge and brakepawl to the positioning member.

Alternatively, the upper end of the positioning member may include afork structure adapted to connect to the shaft at two points on eitherside of inner arm 140. As a further alternative, the positioning membermay include a collar structure such as described above to pivotallycouple around a channel in arbor block 92. In such an embodiment, theupper fork structure of the positioning member may connect to the shafton the side of the inner arm opposite the cartridge provided thecartridge is rotationally coupled to the positioning member by othermeans. Examples of such other mechanisms for rotationally coupling thecartridge and brake pawl to the positioning member are described below.

To replace a spent cartridge 80, shaft 126 is rotated to disengagethreaded portion 150 from the positioning member. The shaft may then bedrawn back through the cartridge. A new cartridge is then placed inposition and the shaft is pushed through the cartridge, positioningmember and inner arm 140. Finally, the shaft is rotated to engagethreaded portion 150 with the positioning member.

It will be appreciated that the embodiments described and depicted abovemay be modified in various ways within the scope of the invention. Forexample, one modification of the embodiment depicted in FIGS. 7-9 isillustrated in FIGS. 10-12. As shown, pivoting support brace 116 hasbeen replaced by a rack assembly 152 mounted on second support member102, and configured to slidably support shaft 126. Rack assembly 152includes an inner bracket portion 154 and an outer bracket portion 156extending outward from the second support member generally parallel toblade 40 and on either side of the blade. Each bracket portion defines achannel 158 that extends generally parallel to table 84. Each ofchannels 158 are sized to receive one of opposite ends of shaft 126 sothat the shaft may slide within the channels as the blade is raised andlowered.

Positioning member 130 is coupled between arbor 42 and shaft 126 tomaintain a constant radial distance between the shaft and the arbor. Asdescribed above, the cartridge and/or brake pawl is rotationally coupledto the positioning member to maintain a constant orientation between thebrake pawl and the perimeter of the blade. Since rack assembly 152 ismounted to second support member 102, the rack assembly, cartridge andbrake pawl are tilted with the blade. Thus, the brake pawl can bemaintained in close proximity to the edge of the blade regardless of theposition of the blade.

When a dangerous condition is detected and brake pawl 60 is pivoted intothe blade, at least a portion of the force of the moving blade istransferred to rack assembly 152. It is believed that the angularmomentum of the blade will tend to urge the blade to move downward asthe blade climbs down the face of the brake pawl. The clockwise (asviewed in FIGS. 10 and 11) angular momentum of the blade is at leastpartially transferred to positioning member 130 which links arbor 42 andshaft 126. Thus, shaft 126 is urged to move in a clockwise directionabout the arbor. Since the shaft is constrained to move horizontally byrack assembly 152, the shaft tends to move toward first support member100, thereby pushing the arbor downward. As a result, brake mechanism 28is configured not only to stop the rotation of the blade, but also to atleast partially retract the blade away from the user's body. Typically,blade 40 is prevented from significant downward retraction by theengagement of first worm gear control member 98 with gear segment 96.Alternatively, at least a portion of first worm gear control member 98may be configured to release gear segment 96 to allow the arbor block topivot downward, thereby retracting the blade below table 84.

It will be appreciated that the embodiment depicted in FIGS. 10-12 maybe modified in a variety of ways within the scope of the invention. Forexample, rack assembly 152 may be positioned to connect to shaft 126 ononly one side of blade 40, similar to the embodiment depicted in FIG. 5.As another example, positioning member 130 may be coupled to pivot aboutthe arbor block, similar to the embodiment depicted in FIGS. 5 and 6.

In each of the exemplary embodiments described above cartridge 80 and/orbrake pawl 60 are rotationally coupled to the positioning member. Thisconfiguration maintains the brake pawl in a constant orientationrelative to the perimeter of the blade as the blade is raised orlowered. In the exemplary embodiments, the cartridge is clamped againstthe positioning member to create a frictional coupling. Alternatively,the cartridge and/or brake pawl may be rotationally coupled to thepositioning member in a variety of other ways as well.

For example, FIGS. 13-15 illustrate one alternative embodiment in whichpositioning member 130 includes a bracket 160 adapted to rotationallycouple the cartridge and brake pawl to the positioning member, as wellas align the brake pawl with blade 40. As shown, bracket 160 extendsoutward from the positioning member and generally parallel to thecartridge. A rear portion of the bracket forms a U-shaped enclosure 162adapted to receive at least a portion of the cartridge. Thus, thecartridge is installed by sliding the cartridge onto shaft 126 and thenrotating the cartridge counter-clockwise (as seen in FIG. 13) intoU-shaped enclosure 162 until it engages an electrical connector 164.

Connector 164 is attached via a cable 166 to control subsystem 26 (notshown). The connector is configured to engage a mating connector (notshown) in the rear of cartridge 80 to electrically couple the cartridgeto the control subsystem. Connector 164 is mounted on a set-screw 168that is threaded through the rear of U-shaped enclosure 162. Thus, theuser may adjust the position of the cartridge and brake pawl relative tothe blade by turning set screw 168. Typically, the brake pawl isadjusted to be relatively close to the blade (e.g., ¼-inch, ⅛-inch,1/16-inch, etc.) to minimize the stopping time. In any event, connector164 engages the mating connector in the cartridge securely enough toprevent the cartridge from rotating relative to the positioning member.Alternatively, connector 164 may be omitted and set-screw 168 may engagethe cartridge directly. In which case, the cartridge may be electricallycoupled to the positioning member by some other mechanism.

FIGS. 16 and 17 show another alternative mechanism adapted torotationally couple the cartridge and brake pawl to the positioningmember. In this embodiment, positioning member 130 includes a bracket170 that extends generally parallel to cartridge 80. The cartridge isslid onto shaft 126 against bracket 170. A locking screw 172 is insertedthrough a hole in the cartridge and into a circular track 174 formed inbracket 170. A wing nut 176 or similar device engages the end of lockingscrew 172 adjacent the bracket. Once the cartridge and brake pawl arerotated to the desired orientation relative to the blade, wing nut 176is tightened to clamp the cartridge to the bracket.

Another alternative mechanism adapted to rotationally couple thecartridge and brake pawl to the positioning member is illustrated inFIG. 18. As shown, at least a portion of shaft 126 is serrated orotherwise non-circularly shaped (e.g., hexagonal, octagonal). The borethrough positioning member 130 adapted to receive the shaft is similarlyserrated or shaped so that shaft 126 is rotationally coupled to thepositioning member. Likewise, the bore through cartridge 80 is serratedor shaped to grip the shaft and prevent rotation relative to the shaftand positioning member. In contrast, brake pawl 60 includes a circularbore adapted to rotate about the shaft when triggered. Prior to beingtriggered however, the brake pawl is held stationary relative to thecartridge and therefore rotates with the positioning member. Similarly,in embodiments where support brace is coupled to the shaft (e.g., suchas shown in FIGS. 4-8), the upper end of the support brace includes acircular bore to rotate about the shaft. Alternatively, the shaft may becircular in cross-section where it is coupled to the support brace.

As described above, the present invention provides an improved safetysystem for use on power tools such as a table saw. The invention isconfigured to detect the occurrence of a dangerous condition and stopthe motion of the blade before a user suffers a serious injury.Optionally, the safety system may be configured to retract the bladeaway from the user. In view of the several embodiments that have beendescribed above, it will be appreciated that the present invention isnot limited to any specific embodiments, but rather encompasses manydifferent configurations, variations and modifications such as will beevident to those of skill in the art. Many such configurations,variations and modifications are described in more detail in thereferences incorporated above, as well as PCT Patent Application SerialNo. PCT/US00/26812, filed Sep. 29, 2000; U.S. Provisional PatentApplication Ser. No. 60/233,459, filed Sep. 18, 2000; U.S. ProvisionalPatent Application Ser. No. 60/225,210, filed Aug. 14, 2000; U.S.Provisional Patent Application Ser. No. 60/225,058, filed Aug. 14, 2000;U.S. Provisional Patent Application Ser. No. 60/225,057, filed Aug. 14,2000; and U.S. Provisional Patent Application Ser. No. 60/157,340, filedOct. 1, 1999.

It is believed that the disclosure set forth above encompasses multipledistinct inventions with independent utility. While each of theseinventions has been disclosed in its preferred form, the specificembodiments thereof as disclosed and illustrated herein are not to beconsidered in a limiting sense as numerous variations are possible. Thesubject matter of the inventions includes all novel and non-obviouscombinations and subcombinations of the various elements, features,functions and/or properties disclosed herein. No single feature,function, element or property of the disclosed embodiments is essentialto all of the disclosed inventions. Similarly, where the claims recite“a” or “a first” element or the equivalent thereof, such claims shouldbe understood to include incorporation of one or more such elements,neither requiring nor excluding two or more such elements.

It is believed that the following claims particularly point out certaincombinations and subcombinations that are directed to one of thedisclosed inventions and are novel and non-obvious. Inventions embodiedin other combinations and subcombinations of features, functions,elements and/or properties may be claimed through amendment of thepresent claims or presentation of new claims in this or a relatedapplication. Such amended or new claims, whether they are directed to adifferent invention or directed to the same invention, whetherdifferent, broader, narrower or equal in scope to the original claims,are also regarded as included within the subject matter of theinventions of the present disclosure.

1. A table saw comprising: a frame including a table defining a planarwork surface, where the table has a front and a back; an arbor supportedby the frame; a rotatable blade on the arbor and extendable up throughthe work surface; a feed direction extending parallel to the plane ofthe work surface from the front to the back of the table so that a usercan place a work piece on the table in front of the blade and slide thework piece in the feed direction toward the back of the table to contactthe blade and cut the work piece; an adjustment mechanism configured toselectively raise and lower the blade relative to the table withoutchanging the angle of the blade relative to the work surface; a brakemechanism configured to engage and stop the blade; and a brakepositioning system configured to maintain the brake mechanism in aconstant orientation adjacent the perimeter of the blade and downstreamof the arbor relative to the feed direction as the blade is raised andlowered relative to the table.
 2. The table saw of claim 1 where thebrake positioning system is configured to prevent the brake mechanismfrom raising and lowering relative to the table when the blade is raisedand lowered.
 3. The table saw of claim 1, where the brake positioningsystem is configured to move at least a portion of the brake mechanismaround the perimeter of the blade when the blade is raised and lowered.4. The table saw of claim 1, where the brake positioning system includesa rack assembly.
 5. The table saw of claim 1, further comprising adetection system configured to detect a dangerous condition between aperson and the blade, and where the brake mechanism is configured toengage and decelerate the blade upon detection of the dangerouscondition.
 6. The table saw of claim 5, where the dangerous condition iscontact between a person and the blade.
 7. The table saw of claim 5,where the dangerous condition is proximity between a person and theblade.